No key support levels for the U.S. market have been broken, even short-term, and we remain in the market's favorable season.Nevertheless, those following a strategy based on buying low and selling high would be wise to have plans in place to execute whatever is their exit strategy fairly quickly this year.If global markets recover, and the U.S. bull market continues, investors need not execute those plans. However, it is usually too late to wait until a market is in the full throes of a significant decline to begin to think about how to handle it.Even though the U.S. market is demonstrating impressive resilience, it has gone nowhere for three months. The rising tide of global market declines is raising the risk that it will not be able to endure against that tide much longer.